Is this really backlash ?

Discussions and help on this commercial controller.

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Re: Is this really backlash ?

Postby gavztheouch » Sat Apr 21, 2012 3:39 pm

Just ran this test again, this time I placed and a vertical line just above the first "snake". If you make the laser cut this vertical line first it takes up the backlash before it begins the cutting the snakes. I don't have a picture but it visualises the backlash in the system better as the start and end cuts of the snake no longer match up.
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Re: Is this really backlash ?

Postby StigOE » Sun Apr 22, 2012 8:59 am

I don't really see how this could be backlash, as the top and bottom horizontal lines are lined up while the lines inbetween are not.
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Re: Is this really backlash ?

Postby gavztheouch » Sun Apr 22, 2012 10:12 am

I don't really see how this could be backlash, as the top and bottom horizontal lines are lined up while the lines inbetween are not.


If the laser head starts in the bottom left or right corner then this is how you would expect the results to look like if you had some backlash in your machine.
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Re: Is this really backlash ?

Postby orcinus » Sun Apr 22, 2012 1:55 pm

That actually makes perfect sense, now that i think about it...
If the backlash is the same in both Y directions, the start and the end *would* match perfectly on both snakes.

The first snake would "lose" as much travelling -Y as the second would travelling +Y. Meaning lengths of both snakes would be the same. And since end of - snake is the beginning of the + snake, both ends would match.
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Re: Is this really backlash ?

Postby iGull » Sun Apr 22, 2012 3:46 pm

Hi Gav et al

Ok on the backlash - that's why I used arcs the second time - you can instantly get your head around the problem when you see the flatened arc section at the start - its obvious that the Y is either taking up backlash slack, or has insufficient torque to accelerate quickly enough.
Using the rectangular snake was perhaps not a good selection (unless you are sharp enough to realise that the resultant effect _is_ backlash - doh :oops: )

I ordered a beefier driver the other day, so should hopefully arrive tomorrow (Mon). Not sure what I'll do if the results are the same after fitting 'though :D

Regarding your doubled backlash Gav, isn't it the case that your dial gauge was measuring actual backlash in Y - the graphical measurement between opposing rectangles will be 2x backlash (Y+ + Y-) ?

Cheers

Neil
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Re: Is this really backlash ?

Postby gavztheouch » Sun Apr 22, 2012 6:51 pm

Regarding your doubled backlash Gav, isn't it the case that your dial gauge was measuring actual backlash in Y - the graphical measurement between opposing rectangles will be 2x backlash (Y+ + Y-) ?


Not sure, why do you think it should be double?
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Re: Is this really backlash ?

Postby iGull » Mon Apr 23, 2012 4:27 pm

Hi

Fixed at last !!!!!

It wasn't the stepper driver current, it was the %$£@!! shaft couplers!
I had bought two 6.35/8.0mm shaft couplers - used them loads of times - in a different axial mode of course :oops:

I fitted the new stepper driver and upped the current - very slight improvement, but nothing great - upped the current again and the stepper started driving rough. Backed off the current again.
Took a step back now that I had more info - I had already replaced the shafts and bearings, so it could only be the motor or couplers. Decided to rip out the couplers and turn down a pair of solid new ones - refitted - bingo, instant success - best circles I've seen from the machine and the rectangular snake test is exactly 60mm long to boot :-)
Obviously there has been compliance in the Y drive shaft - why didn't I think of that before - back to Tim's sig I guess :lol:
I'm a happy bunny today - I'll maybe see if I can find some pro versions with clamps rather than the screw type I turned up.
It's been a pain, but a good exercise.

Here's a pic of the originals ...
shaft coupler.JPG
Shaft coupler

Hope this will maybe help someone else in the future.

Thanks to all for their help and comments.

Cheers

Neil
Last edited by iGull on Mon Apr 23, 2012 8:26 pm, edited 1 time in total.
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Re: Is this really backlash ?

Postby maralb » Mon Apr 23, 2012 5:40 pm

also I had problems with backlash
it had been written in this post the guilt the shaft couplers
http://www.lightobject.info/viewtopic.php?f=47&t=737
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Re: Is this really backlash ?

Postby gavztheouch » Mon Apr 23, 2012 7:55 pm

I also have flexible coupling problems with my build, I bought these on Saturady

http://www.ebay.co.uk/itm/220949342859?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_678wt_1139n

Hopefully they will be here tomorrow so I can see if it solves my backlash blues.
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Re: Is this really backlash ?

Postby iGull » Mon Apr 23, 2012 8:25 pm

maralb wrote:also I had problems with backlash
it had been written in this post the guilt the shaft couplers
http://www.lightobject.info/viewtopic.php?f=47&t=737


Grazie Maralb, funny how the solution pops up after you find it eh ?
I checked lightobjects website too - not a single word of backlash on this thread - no wonder searching missed it :oops:

OK on the shaft couplers Gav, they look perfect. I checked evilbay too and couldn't find solid couplers - I never check with mar$hantdi$e because they are always so expensive ;) I saw them here too ...

http://www.cnc4you.co.uk/index.php?rout ... duct_id=48

I may just get the marchantdice ones - they have the correct size for me 6.35/8mm.

Cheers

Neil
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